1. Field of the Invention
The present invention relates to a variable displacement, swash plate type compressor for use in an air-conditioner for air-conditioning vehicle compartment. More particularly, it relates to a control mechanism for changing the displacement of a compressor by changing an angle of wobble of a swash plate assembly so that pistons in the compressor can be driven in association with a change in a cooling load within an air-conditioned area, i.e. the vehicle compartment.
2. Description of the Related Art
Generally, a swash plate type compressor is provided with a plurality of cylindrical bores (cylinders) arranged circumferentially around the center of rotation of a swash plate, with a plurality of pistons slidably fitted in associated cylinders, respectively, and reciprocated by the wobbling motion of the rotating swash plate so that the reciprocating pistons successively pump a refrigerant gas into and compress the same within the cylinder bores. To vary the displacement of such swash plate type compressor in association with a change in a cooling load, a control system is conventionally employed for changing the wobble angle of the rotary swash plate in compliance with a change in a suction pressure which accompanies a change in a cooling load within a closed space to be air-conditioned, such as a vehicle compartment.
Two typical control systems for changing the wobble angle of a rotary swash plate of a variable displacement swash plate type compressor are disclosed in U.S. Pat. No. 4,428,718 to Skinner and U.S. Pat. No. 4,037,993 to Roberts.
In the control system of the former U.S. Patent, the wobble angle of the swash plate that is directly related to the compressor displacement is controlled by a crankcase-suction pressure differential. The control system has a displacement control valve, responsive to both compressor suction and discharge pressure, arranged to provide controlled communication of same with the compressor crankcase so that the compressor displacement, and thus the discharge flow rate, is increased with an increase in discharge pressure and with an increase suction pressure.
In the variable displacement, swash plate type compressor of the latter U.S. Patent, the control system includes a fluid actuator for shifting a centering ball on which the cam mechanism is supported, to effect a change in the piston stroke length by varying the angle of inclination of the wobbling swash plate with respect to the drive shaft axis of the compressor.
However, in the former control system, a non-rotary wobble plate joined to a rotary swash plate via needle bearings is operatively connected to a lug member radially projecting from a drive shaft by the engagement of a cross pin in a guide slot formed in the lug member. Thus, the accuracy of control of the angle of inclination of the wobble and swash plates is insufficient. Also, the engagement of the cross pin and the lug member lacks mechanical durability against a compression reaction force caused by the pistons. Further, wear is apt to occur at the engaging portion of the cross pin and the guide slot of the lug member, resulting in the occurrence of unfavorable play in the mechanism for changing the wobble angle of the wobble and swash plates. As a result, stability of the repeated reciprocatory motion of the pistons cannot be ensured over a long period.
In the latter control system, link and pin members are employed for connecting a swash plate assembly to a drive shaft assembly of the compressor. Accordingly, it is difficult to achieve a high accuracy of control of the wobble angle of the swash plate assembly. Also, such a connecting mechanism consisting of link and pin members is insufficient for long-term mechanical durability against a compression reaction force caused by the reciprocatory pistons. In addition, the control system of the latter U.S. Patent has a complicated mechanical construction, reducing reliability in the operation thereof.